docs: def convert2wavenumber(self):
          """Convert from wavelengths to wavenumber"""
          for chname in self.rsr.keys():
              elems = [k for k in self.rsr[chname].keys()]
              for sat in elems:
                  if sat == "wavelength":
                      LOG.debug("Get the wavenumber from the wavelength: sat=%s chname=%s", sat, chname)
                      wnum = 1. / (1e-4 * self.rsr[chname][sat][:])  # microns to cm
                      self.rsr[chname]['wavenumber'] = wnum[::-1]
                  else:
                      if type(self.rsr[chname][sat]) is dict:
                          for name in self.rsr[chname][sat].keys():
                              resp = self.rsr[chname][sat][name][:]
                              self.rsr[chname][sat][name] = resp[::-1]
                      else:
                          resp = self.rsr[chname][sat][:]
                          self.rsr[chname][sat] = resp[::-1]
  
          for chname in self.rsr.keys():
              del self.rsr[chname]['wavelength']
  
          self.unit = 'cm-1'